A couple of SU questions

[dutchzcarguy]

13 hours ago, grannyknot said:

looking around for an article or vid that gives all the baseline measurements/settings and tricks to get the nozzle centred.

How about the original servicemanual?  😁

[Mark Maras]

 When centering the needles, screw the nozzles all the way up to the top. If the needle encounters resistance at closed throttle and you can't get it perfect, lower the nozzles to the running position (2 1/2 turns down) and it's likely they'll be fine.

[siteunseen]

17 hours ago, Yarb said:

@siteunseenTime to hit the library!!!

Grannyknot wrote the books on 240s, I only know how to read them. 

 

 

 

[Captain Obvious]

On 11/1/2023 at 5:17 PM, grannyknot said:

I have been looking around for tricks to get the nozzle centred.

Most of the methods I've seen tossed about can get the nozzle "close", but aren't great. It's really difficult to discern when the needle is rubbing against the nozzle. I made a special tool (surprised?) to re-establish the alignment nub positioning on the 3-screw roundtops as well as the flat-tops, but it also works great for nozzle positioning on the 4-screw round tops.

That said, since you have a lathe, I think you could get close enough with something simpler. Make yourself a short "alignment needle". Should really have a picture, but I'll try to use just words:

Chuck up a piece of 4mm dia (or larger) brass in your lathe and turn a 20mm length down to .125" diameter. Make it so it just barely fits into the suction piston hole like the needle does. Close tolerance fit, but not a press fit. Then continue to turn down a 10mm length down to .100" so it just barely fits into the nozzle hole. Make sure you do both of those operations without taking the piece out of the chuck. That will ensure that the two different diameters are concentric. Then.... cut it off and debur any kicked up areas if necessary. You should have a 20mm long piece of brass that is .125" at one end and .100" at the other end. This is your stubby alignment needle.

Install the alignment needle into the suction piston.
Loosen (really loose) the nozzle alignment nut.
Put the suction piston (with alignment stub installed) into the carb body making sure the stub goes correctly into the nozzle hole.
Install the round top cover and tighten the screws.

Tighten the nozzle nut. The nozzle should now be aligned with the center of the suction piston, but you can verify the alignment by lifting the suction piston and letting it back down gently. If the needle is properly aligned, it will re-enter the hole in the nozzle smoothly without catching on the side of the hole. If the stub needle doesn't enter smoothly, it's because the nozzle position shifted a little bit when you tightened the lock nut.

Repeat the loosening and re-tightening of the nozzle lock nut as necessary until the stub needle enters the hole properly without catching on the side of the hole. *

Take the cover off and pull out the piston. Remove the alignment stub and install the real needle in it's place. When you put everything back together, the nozzle should be aligned with the center of the suction piston.

Does that make sense?

* And this is one of the reasons the typical methods of aligning the nozzle using a normal needle fails. The tapered lead in of the normal needle will always enter the hole even if the nozzle is misaligned. It may rub against the needle near the hilt, but you may never notice a small amount of interference.

Edited November 5, 2023 by Captain Obvious

[siteunseen]

A new tool huh? Would you make this girl a smaller guitar? About a violin size. 

 

[Captain Obvious]

@grannyknot

I added a step in the alignment procedure above. You should test to make sure the nozzle didn't squirm around as you tightened the lock nut.

[Captain Obvious]

On 11/2/2023 at 2:21 PM, siteunseen said:

A new tool huh? Would you make this girl a smaller guitar? About a violin size. 

Haha! I'll get right on that!